Vertical redistribution of zooplankton in an oligotrophic lake associated with reduction in ultraviolet radiation by wildfire smoke

Abstract

We used a natural experiment to test whether wildfire smoke induced changes in the vertical distribution of zooplankton in Lake Tahoe by decreasing incident ultraviolet radiation (UV). Fires have a variety of effects on aquatic ecosystems, but these impacts are poorly understood and have rarely been observed directly. UV is an important driver of zooplankton vertical migration, and wildfires may alter it over large spatial scales. We measured UV irradiance and the distribution of zooplankton on two successive days. On one day, smoke haze from a nearby wildfire reduced incident UV radiation by up to 9%, but not irradiance in the visible spectrum. Zooplankton responded by positioning themselves, on average, 4.1 m shallower in the lake. While a limited data set such as this requires cautious interpretation, our results suggest that smoke from wildfires can change the UV environment and distribution of zooplankton. This process may be important in drought‐prone regions with increasingly frequent wildfires, and globally due to widespread biomass burning.

The interactive effects of stratospheric ozone depletion, UV radiation, and climate change on aquatic ecosystems

“…Thus, when winds brought a smoke plume from large California wildfires over Lake Tahoe, zooplankton, which use UV radiation as a depth cue, 75 migrated to shallower depths, potentially affecting their susceptibility to plankton-eating fish predators. 212…”

“…92,131,159 The strength of the response is related to size, level of pigmentation, and previous exposure to UV radiation of the organisms, 92,104,159 . Behavioural responses to exposure to UV radiation are relatively quick, on the order of seconds and minutes (see also Chapter 3 and refs 104,159,235 ) suggesting that short-term shifts in UV exposure due to changes in cloud cover, sun angle, or other factors, such as UV-absorbing DOM or haze from smoke, can affect the exposure and thus the vertical distribution of zooplankton 92,212,235 and their availability as food for fish (see also Chapters 1, 5, and 6) for more on UV radiation and wildfires).…”

Do lakes feel the burn? Ecological consequences of increasing exposure of lakes to fire in the continental United States

“…;Lewis et al, 2014). Reduced UV exposure due to smoke can redistribute zooplankton to shallower depths (Figure 4c;Urmy et al, 2016).Increases in primary productivity, however, are mediated by light availability, which may increase or decrease depending on DOC or sediment concentrations in runoff and vegetation loss near lakes and/or tributaries(Figure 4a,g;McEachern et al, 2000;Rhoades et al, 2011), and water temperatures and thermal structure, which also depend on vegetation loss, as well as wind exposure(Figure 4b…”

Seasonal changes in the biomass, distribution, and patchiness of zooplankton and fish in four lakes in the Sierra Nevada, California

“…Both the drought and Rim Fire are likely to have affected the lakes. Fires can increase runoff from burned catchments, deposit ash from the air, or alter the characteristics of incident solar radiation via drifting smoke plumes (Urmy et al., ; Williamson et al., ), although their effects on a lake's zooplankton are not necessarily large (Patoine, Pinel‐Alloul, & Prepas, ). While the drought probably contributed to the fire's severity, it may have actually mitigated some of the fire's effects on Cherry and Eleanor: precipitation during the winter of 2013–2014 was well below normal (California Department of Water Resources, ), meaning that runoff and erosion in the burned areas were much less than they might have been in a more normal year.…”